In general, those skilled in the art are convinced that purified naphthalene is essential to the condensation of naphthalene sulphonates: As stated in Kirk-Othmer; Encyclopedia of Chemical Technology 3rd edition Volume 15, page 715, "Approximately 5.7% of the U.S. naphthalene supply is consumed in the manufacture of tanning agents. These are derivatives of naphthalene sulfonic acids, their salts, and the sodium salts of the reaction products of the sulfonic acid and formaldehyde. Both petroleum and purified coal-tar naphthalene are used in these processes." In other words, and as is well known by those skilled in the art, in order to obtain satisfactory products, it is the general belief that purified naphthalene derived from coal-tar or petroleum have to be used which means naphthalene obtained from redistillation and/or recrystalization of the crude feed-stock.
"Naphthalene sulfonates represent another small outlet for naphthalene i.e. 1% of supply. The products are used as wetting agents and dispersants in paints and coatings and in a variety of pesticide and cleaner formulations. Their application as surfactant is expected to continue as a low growth item, although recently use of these products as concrete additive, i.e. plasticizers, may alter this pattern".
On page 720, of Kirk-Othmer as referred to above the methods of making 2-naphthalene sulfonic acids are disclosed wherein: naphthalene is reacted at a temperature above 150.degree., (160.degree.) using in excess 96% H.sub.2 S0.sub.4 to produce 2-naphthalene sulfonic acid (2-NSA).
In general, large excess of sulfuric acid is used such as 20-30%, and preferably 25% by weight on pure naphthalene for the sulfonation which extends over a period of 6 to 7 hours. Then polycondensation is carried out for a period of 36 hours and over at a temperature below 100.degree. C., after further addition of concentrated sulphuric acid, thus increasing the total excess to 100-105 mole percent. The reaction product is the neutralized with calcium hydroxide and caustic soda (NaOH). The polycondensate is then filtered to remove the large amount of salt obtained by neutralization, the filtration requiring about 26 hours.